Login Problem

I am using Vbulletin 4 for my forum and vBSEO 3.6.0.

And when I click on Reply to thread without login then it takes me to this page.
vBulletin Message

And after entering username and password it first gives the message "thank you for login" and then gives the message
Page not found"
http://college-chat-rooms.gradchat.net/%7B$vbulletin-%3Eurl%7D

Login is working fine from navigation bar but it gives issue only if someone click on reply to thread and then put login info.

This is my actual forum url
http://college-chat-rooms.gradchat.net/forum/

Please help me out why I am having this issue.

Hello,

Support is offered for verified vBSEO customers only. If you hold a valid license, please open a ticket with your transaction ID from your payment receipt along with your forum URL so we can assign it to your account:
vBSEO.com Helpdesk.

If you are working on behalf of someone else as a contractor, they need to add you to their Priority Support list:
Customer Profile.